Temperature Of Spontaneous Combustion Research Articles

An investigation of the factors associated with interpretation of mine atmosphere for spontaneous combustion in coal mines

The risk of spontaneous combustion of coal is highly serious especially in gaseous underground coal mines. In many cases such a spontaneous combustion is a source of initiation of methane-explosive mixture with tragic consequences. Early indication of spontaneous combustion and determination of its seat temperature is in a given environment a key part of safety of underground coal mines. A commonly used method for the detection of spontaneous combustion is an interpretation of coal oxidation gas products whose historical roots go back to the first halve of the 20th century as Graham's ratio. In the second half of this century a wide research on application of desorbed higher hydrocarbons C1–C4 and hydrogen for the given purpose took place. Until now, the interpretations in question encounter significant inaccuracies. The paper describes the research on factors affecting the accuracy of the determination of coal spontaneous combustion temperature on conditions of underground coal mines. The research was focused on the accuracy of interpretation of mine gases in connection with the use of laboratory verified gas characteristics of thermal oxidation of coal. Three chromatograph laboratories had been involved to test thermal oxidation of coal to determine a deviation of spontaneous combustion gases. The variability among the laboratories and used techniques were insignificant. Besides the laboratory methods, it may not reflect processes in coal mines and one of the results was that coal itself had been a source of substantial variability of desorption of spontaneous combustion gases. The spontaneous combustion data still requires human interpretation. Simple criteria for providing warning by a computer do not exist just yet.

Coal proximate analyses correlations with airborne respirable dust and spontaneous combustion temperature

Coal proximate analyses correlations with airborne respirable dust and spontaneous combustion temperature

High-temperature oxidation and spontaneous combustion of rare-earth metal powders

In this paper, attempts are made to correlate the temperature of spontaneous combustion of rare-earth metal (REM) powders with the oxidation reaction mechanism in air. Tests were made on the three most oxidation-resistant powders, scandium, yttrium, and lanthanum. The powders were prepared by grinding the solid metals in an atmosphere of purified argon, with subsequent sieving. The dimensions of the particles in the test samples ranged from 50 to 250 micrometers. It is found that the oxidation mechanism changes with increasing temperature and that a characteristic of these particular powders is the existence of a limited temperature range over which the oxidation reaction follows a linear law. Yttrium powder has the lowest temperature at which oxidation becomes discernible.

Inflammability of zirconium powders and its alloys in the suspended state

1. The values of the lower concentration limits of inflammability (LCL) of aerosols of Zr, Ti, Si, and alloys Zr-Ti and Zr-Si were determined. 2. The character of the dependence of the LCL of aerosols on the alloy's composition coincides with the character of this dependence for the temperature of spontaneous combustion of powder in a layer, which is related with the constitution diagram of the alloy. Inflammability of an alloy is determined primarily by its chemical activity. The induction period and flame propagation rate are also determined by the alloy's activity. 3. Burning of the investigated alloys probably occurs on the surface of molten particles. Oxygen is dissolving in the liquid metal and, when the solubility limit is reached, the oxide phase crystallizes from the melt. As solid films are accumulated, the reaction is slowed down and stops when the liquid-metal phase disappears. Silicon, owing to its high volatility, burns in the vapor phase. 4. The method of partial filling of a spherical bomb with aerosol permits obtaining homogeneous aerosols in a wide range of concentrations and using thin-walled glass bombs facilitates the use of optical methods of investigation.

Combustibility of metal powder

1. A microstructural analysis of the combustion products of powders of zirconium and its alloys confirms the previously proposed [1] two-stage mechanism of ignition with diffusion of oxygen through the solid oxide film at the first stage and with dissolution of the oxide film in the second, liquid-metal phase. 2. An equation is derived from the thermal balance of powder oxidation which relates the temperature of spontaneous combustion with the physicochemical characteristics of the specimen and satisfactorily agrees with the experimental data. 3. Storage of powders in the air has a different effect on their combustibility, which is explained by the characteristics of the kinetics of the growth of the oxide films. For alloys with high chemical activity (Zr-Ti) and low (Zr containing more than 50% Si) six-months' storage does not change the temperature of spontaneous combustion.